FIG. 1 illustrates a data communication flow between two User Equipments (UEs) in traditional cellular communication technologies, where voice, data and other service of the two user equipments are exchanged through respective evolved Node B's (eNBs) where they are camping on, and a core network.
The technology of Device-to-Device (D2D), i.e., direct communication between user equipments, refers to a scheme in which the adjacent user equipments can transmit data in a short-distance range over a direct connection link without forwarding through any central node (i.e., an eNB), as illustrated in FIG. 2. The D2D technology has the following advantages due to its short-distance communication characteristic and direct communication scheme:
The user equipments can communicate directly over a short distance at a relatively high data rate, a relatively low delay, and relatively low power consumption;
Spectrum resources can be utilized efficiently using the user equipments widely distributed in the network, and the short-distance characteristic of the D2D communication link;
The D2D direct communication scheme can be adapted, for example, for a demand of sharing local data for wireless P2P and other services, to provide data services with a flexible adaptation capacity; and
D2D direct communication can extend a coverage area of the network using a large number of communication user equipments widely distributed in the network.
For the problem of inter-interference with the cellular network when there is network coverage: an influence upon the user equipments in the traditional cellular network when there is network coverage will be alleviated as much as possible, as illustrated in FIG. 3.
In the LTE system, although the base station can operate as a central controller in the LTE to schedule reasonably communication between the D2D user equipments, if there is a high load in the LTE system, thus resulting in significant interference, then there will be no mechanism to guarantee that a D2D user equipment in the LTE system is D2D-switched under reasonable conditions to another distinct system with the guaranteed quality of transmission over a short distance.
In summary, if there is a high load in the LTE system, thus resulting in significant interference, then there has been absent so far a mechanism to enable a D2D user equipment to perform D2D-switching under reasonable conditions to guarantee the quality of transmission over a short distance.